This invention relates to the clamping of work pieces and other items required to be held in place while work is performed, and is particularly directed to an improved clamp arm for mounting on the plunger of a clamping cylinder.
Power assisted clamping devices are used to hold work pieces on the work tables in a machining operation or an automatic assembly operation. The clamping devices typically include a pneumatic or hydraulically operated cylinder which raises and lower a plunger to which is attached a clamp arm that engages the work piece and hold it securely in place. The cylinder may function to simply raise or lower the plunger, and thereby the clamp arm, or may also function to rotate the plunger as it is moved axially to thereby swing the clamp arm out of the way for ease of withdrawal and replacement of the work piece.
It is desirable to mount the clamp arm on the plunger in a manner that allows the clamp arm to be positioned at any point about the perimeter of the plunger while being locked in the selected peripheral position and being restrained axially on the plunger. Such mounting is typically accomplished by holding the clamp arm on the end of the plunger by use of a capscrew threaded into an axial bore in the end of the plunger.
The plunger is subjected to a number of loads, both those caused by the clamping forces and those resulting from the method of mounting. The clamping forces will exert a bending load on the top of the plunger because the arm engages the work piece at a point spaced from the axis of the plunger. Mounting the clamp arm through use of a capscrew threaded into an axial bore in the plunger end reduces the effective cross-section of the plunger and thereby reduces its ability to withstand the bending forces. Using a capscrew to mount the clamp arm on the plunger also introduces torque loads on the plunger. This may be undesirable, particularly if the plunger is a part of a cylinder which both axially moves and rotates to swing the clamp arm.
The present invention eliminates the application of a torque load on the plunger in the mounting of the clamp arm and also maximizes the bending load capacity of the plunger.